Hybrid chiral domain walls and skyrmions in magnetic multilayers

Noncollinear spin textures in ferromagnetic ultrathin films are currently the subject of renewed interest since the discovery of the interfacial Dzyaloshinskii-Moriya interaction (DMI). This antisymmetric exchange interaction selects a given chirality for the spin textures and allows stabilising configurations with nontrivial topology. Moreover, it has many crucial consequences on the dynamical properties of these topological structures, including chiral domain walls (DWs) and magnetic skyrmions. In the recent years the study of noncollinear spin textures has been extended from single ultrathin layers to magnetic multilayers with broken inversion symmetry. This extension of the structures in the vertical dimension allows very efficient current-induced motion and room-temperature stability for both N\'eel DWs and skyrmions. Here we show how in such multilayered systems the interlayer interactions can actually lead to more complex, hybrid chiral magnetisation arrangements. The described thickness-dependent reorientation of DWs is experimentally confirmed by studying demagnetised multilayers through circular dichroism in x-ray resonant magnetic scattering. We also demonstrate a simple yet reliable method for determining the magnitude of the DMI from static domains measurements even in the presence of these hybrid chiral structures, by taking into account the actual profile of the DWs. The advent of these novel hybrid chiral textures has far-reaching implications on how to stabilise and manipulate DWs as well as skymionic structures in magnetic multilayers.Comment: 22 pages, 5 figure

Une approche sociocritique des usages numériques en éducation

International audienceThis article aims to contribute to formalize a sociocritical approach of digital technology in education. Such a sociocritical approach focuses on the relationships between students’ sociocultural profiles and contexts, and their disposition to learn with digital technology. This approach lies at the crossroads of sociology of use, on the one hand, which has granted little attention to educational uses of digital technology, and, on the other hand, education sciences, which have mainly considered educational uses of digital technology within the school context. It is part of the theme of educational uses of digital technology (Baron, 2014) and it is complementary to didactic and psychopedagogical approaches of digital technology, which are more commonly used. We first explain the foundation of this approach of digital technology in education. We then present an overview of three main research interests of this approach, before discussing its methodological implications, its complementarity with educational technology approaches and the challenges that are raised.■ RÉSUMÉ • Cet article a pour objectif de contribuer à formaliser une approche sociocritique du numérique en éducation. Telle que nous la concevons, cette approche consiste à étudier les relations entre le profil et le contexte socioculturel des élèves et leur disposition à s'éduquer et se former avec le numérique. Elle se situe au croisement, d'une part, de la sociologie des usages, qui a peu développé les dimensions éducatives du numérique, et d'autre part, des sciences de l'éducation, qui ont faiblement mis en lien les usages numériques proposés aux élèves en salle de classe avec ceux développés en contexte extrascolaire. Elle s'inscrit dans la thé-matique des usages numériques éducatifs, telle que circonscrite par (Baron , 2014), et se veut complémentaire aux approches didactique et psychopédagogique majoritairement utilisées. Nous commençons par expliciter les fondements de cette approche. Nous présentons ensuite un aperçu de trois de ses thématiques saillantes, avant d'aborder ses implications méthodologiques et sa complémentarité avec les approches didacti-que et psychopédagogique, ainsi que les principaux défis qu'elle doit relever. ■ MOTS-CLÉS • Approche sociocritique, rapport éducatif au numérique, contexte extrascolaire

Electrical signature of individual magnetic skyrmions in multilayered systems

Magnetic skyrmions are topologically protected whirling spin textures that can be stabilized in magnetic materials in which a chiral interaction is present. Their limited size together with their robustness against the external perturbations promote them as the ultimate magnetic storage bit in a novel generation of memory and logic devices. Despite many examples of the signature of magnetic skyrmions in the electrical signal, only low temperature measurements, mainly in magnetic materials with B20 crystal structure, have demonstrated the skyrmions contribution to the electrical transport properties. Using the combination of Magnetic Force Microscopy (MFM) and Hall resistivity measurements, we demonstrate the electrical detection of sub-100 nm skyrmions in multilayered thin film at room temperature (RT). We furthermore analyse the room temperature Hall signal of a single skyrmion which contribution is mainly dominated by anomalous Hall effect.Comment: 13 pages, 4 figure

Contrasting nutritional acclimation of sugar maple (Acer saccharum Marsh.) and red maple (Acer rubrum L.) to increasing conifers and soil acidity as demonstrated by foliar nutrient balances

Sugar maple (Acer saccharum Marshall, SM) is believed to be more sensitive to acidic and nutrient-poor soils associated with conifer-dominated stands than red maple (Acer rubrum L., RM). Greater foliar nutrient use efficiency (FNUE) of RM is likely the cause for this difference. In the context of climate change, this greater FNUE could be key in favoring northward migration of RM over SM. We used the concept of foliar nutrient balances to study the nutrition of SM and RM seedlings along an increasing gradient in forest floor acidity conditioned by increasing proportions of conifers (pH values ranging from 4.39 under hardwoods, to 4.29 under mixed hardwood-conifer stands and 4.05 under conifer-dominated stands). Nutrients were subjected to isometric log-ratio (ilr) transformation, which views the leaf as one closed system and considers interactions between nutrients. The ilr method eliminates numerical biases and weak statistical inferences based on raw or “operationally” log-transformed data. We analyzed foliar nutrients of SM and RM seedlings and found that the [Ca,Mg,K| P,N] and [Ca,Mg| K] balances of SM seedlings were significantly different among soil acidity levels, whereas they did not vary for RM seedlings. For SM seedlings, these differences among soil acidity levels were due to a significant decrease in foliar Ca and Mg concentrations with increasing forest floor acidity. Similar differences in foliar balances were also found between healthy and declining SM stands estimated from literature values. Conversely, foliar balances of RM seedlings did not differ among soil acidity levels, even though untransformed foliar nutrient concentrations were significantly different. This result highlights the importance of using ilr transformation, since it provides more sensitive results than standard testing of untransformed nutrient concentrations. The lower nutrient requirements of RM and its greater capacity to maintain nutrient equilibrium are factors that could explain its competitive success and recent northward expansion. This study underscores the importance of using nutrient balances to study the redistribution of plant species in natural ecosystems under climate change

ERAU\u27s First Suborbital Payload for Cell Research

Commercial Space Operations and Aerospace Engineering students from Embry-Riddle are working with students and faculty from the University of Texas Health Science Center at San Antonio and Medical University of South Carolina to launch a suborbital payload onboard Blue Origin’s New Shepard rocket during the summer of 2017. This NanoLab experiment, exposed to microgravity, will consist of T-cells primed with different cytokines that may help us expand our understanding of future treatments for terminal diseases. The first team, Operations team, is conducting the physical testing of the NanoLab by measuring the survivability of the payload under extreme conditions of the suborbital flight. This team is developing operational procedures and data collection guidelines for the different mission phases. The data collected includes accelerations in the X, Y, and Z directions, temperature, and relative humidity. The Engineering team is in charge of the design, analysis and development of the 2U cube-structure that will house the experiment and will be capable of withstanding the forces experienced during the suborbital mission

Correlating Molecular Phylogeny with Venom Apparatus Occurrence in Panamic Auger Snails (Terebridae)

Central to the discovery of neuroactive compounds produced by predatory marine snails of the superfamily Conoidea (cone snails, terebrids, and turrids) is identifying those species with a venom apparatus. Previous analyses of western Pacific terebrid specimens has shown that some Terebridae groups have secondarily lost their venom apparatus. In order to efficiently characterize terebrid toxins, it is essential to devise a key for identifying which species have a venom apparatus. The findings presented here integrate molecular phylogeny and the evolution of character traits to infer the presence or absence of the venom apparatus in the Terebridae. Using a combined dataset of 156 western and 33 eastern Pacific terebrid samples, a phylogenetic tree was constructed based on analyses of 16S, COI and 12S mitochondrial genes. The 33 eastern Pacific specimens analyzed represent four different species: Acus strigatus, Terebra argyosia, T. ornata, and T. cf. formosa. Anatomical analysis was congruent with molecular characters, confirming that species included in the clade Acus do not have a venom apparatus, while those in the clade Terebra do. Discovery of the association between terebrid molecular phylogeny and the occurrence of a venom apparatus provides a useful tool for effectively identifying the terebrid lineages that may be investigated for novel pharmacological active neurotoxins, enhancing conservation of this important resource, while providing supplementary information towards understanding terebrid evolutionary diversification

The poxviral scrapin MV-LAP requires a myxoma viral infection context to efficiently downregulate MHC-I molecules

AbstractDownregulation of MHC class I molecules is a strategy developed by some viruses to escape cellular immune responses. Myxoma virus (MV), a poxvirus causing rabbit myxomatosis, encodes MV-LAP that is known to increase MHC-I endocytosis and degradation through a C4HC3 motif critical for an E3 ubiquitin ligase activity. Here, we performed a functional mapping of MV-LAP and showed that not only the C4HC3 motif is necessary for a marked downregulation of MHC-I but also a conserved region in the C-terminal part of the protein. We also showed that the putative transmembrane domains are responsible for a specific subcellular localization of the protein: they retain MV-LAP in the ER in transfected cells and in the endolysosomal compartments in infected cells. We observed that a specific MV infection context is necessary for a fully efficient downregulation of MHC-I. Our data suggest that the functionality of viral LAP factors, inherited by herpes- and poxviruses from mammalian cells, is more complex than anticipated